Nitride semiconductor light-emitting device and method of manufacturing nitride semiconductor light-emitting device

ABSTRACT

A nitride semiconductor light-emitting device including a coating film and a reflectance control film successively formed on a light-emitting portion, in which the light-emitting portion is formed of a nitride semiconductor, the coating film is formed of an aluminum oxynitride film or an aluminum nitride film, and the reflectance control film is formed of an oxide film, as well as a method of manufacturing the nitride semiconductor light-emitting device are provided.

This nonprovisional application is based on Japanese Patent ApplicationsNos. 2006-119500 and 2007-077362 filed with the Japan Patent Office onApr. 24, 2006 and Mar. 23, 2007, respectively, the entire contents ofwhich are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a nitride semiconductor light-emittingdevice and a method of manufacturing a nitride semiconductorlight-emitting device.

DESCRIPTION OF THE BACKGROUND ART

In a nitride semiconductor laser device representing nitridesemiconductor light-emitting devices, in order to control reflectance ata facet of a cavity with respect to laser beams, an AR(Anti-Reflectance) coating film for attaining the reflectance ofapproximately 10% at the facet of the cavity with respect to the laserbeams may be formed on a light-emitting facet of the cavity that shouldserve as a light-emitting portion of the nitride semiconductor laserdevice, and an HR (High-Reflectance) coating film for attaining thereflectance at approximately 80 to 100% with respect to the laser beamsmay be formed on a light-reflecting facet of the cavity (see, forexample, Patent Document 1 (Japanese Patent Laying-Open No. 09-162496),Patent Document 2 (Japanese Patent Laying-Open No. 2002-237648), andPatent Document 3 (Japanese Patent Laying-Open No. 03-209895)).

SUMMARY OF THE INVENTION

Here, in the nitride semiconductor laser device, the threshold value canbe lowered by raising the reflectance at the light-emitting facet of thecavity with respect to the laser beams to thereby lower mirror loss.Meanwhile, as the light-emitting facet of the cavity of the nitridesemiconductor laser device may be broken due to COD (CatastrophicOptical Damage), a COD level (optical output at the time when thelight-emitting facet of the cavity is broken due to COD) should beraised.

If a single layer of a silicon oxide film, an aluminum oxide film, atitanium oxide film, a tantalum oxide film, a zinc oxide film, or thelike is formed as an AR coating film on the light-emitting facet of thecavity of the nitride semiconductor laser device, however, improvementin the reflectance at the light-emitting facet of the cavity has notbeen sufficient. Alternatively, if a multi-layer film formed of a stackof an aluminum oxide film and a silicon oxide film is formed as an ARcoating film in contact with the light-emitting facet of the cavity, theCOD level has been low.

Moreover, as optical density at the light-emitting facet of the cavityis increased when the reflectance at the light-emitting facet of thecavity is higher, it has been conventionally difficult to achieve higherreflectance at the light-emitting facet of the cavity while maintaininghigh COD level.

From the foregoing, an object of the present invention is to provide anitride semiconductor light-emitting device capable of achieving higherreflectance at a light-emitting facet of a cavity while maintaining ahigh COD level, as well as a method of manufacturing a nitridesemiconductor light-emitting device.

The present invention is directed to a nitride semiconductorlight-emitting device including a coating film and a reflectance controlfilm successively formed on a light-emitting portion, the light-emittingportion being formed of a nitride semiconductor, the coating film beingformed of an aluminum oxynitride film or an aluminum nitride film, andthe reflectance control film being formed of an oxide film.

In addition, preferably, in the nitride semiconductor light-emittingdevice according to the present invention, the reflectance control filmis formed of a stack of an aluminum oxide film and a silicon oxide film.

In addition, preferably, in the nitride semiconductor light-emittingdevice according to the present invention, oxygen content in the coatingfilm is in a range from at least 0 atomic % to at most 35 atomic %.

In addition, preferably, in the nitride semiconductor light-emittingdevice according to the present invention, the light-emitting portionhas reflectance of at least 18% with respect to light emitted from thenitride semiconductor light-emitting device.

In addition, preferably, in the nitride semiconductor light-emittingdevice according to the present invention, an aluminum oxide film and astack of a silicon oxide film and a tantalum oxide film are successivelyformed on a light-reflection side.

In addition, preferably, in the nitride semiconductor light-emittingdevice according to the present invention, an aluminum oxide film and astack of a silicon nitride film and a silicon oxide film aresuccessively formed on a light-reflection side.

Moreover, the present invention is directed to a method of manufacturinga nitride semiconductor light-emitting device including a coating filmand a reflectance control film successively formed on a light-emittingportion, and the method includes the steps of: forming the coating filmformed of an aluminum oxynitride film or an aluminum nitride film on thelight-emitting portion; and forming the reflectance control film formedof an oxide film on the coating film.

In the method of manufacturing a nitride semiconductor light-emittingdevice according to the present invention, a stack of an aluminum oxidefilm and a silicon oxide film is preferably formed as the reflectancecontrol film.

In addition, in the method of manufacturing a nitride semiconductorlight-emitting device according to the present invention, if the coatingfilm is formed of an aluminum oxynitride film, the coating film may beformed by using aluminum oxide as a target.

According to the present invention, a nitride semiconductorlight-emitting device capable of achieving higher reflectance at alight-emitting facet of a cavity while maintaining a high COD level, aswell as a method of manufacturing a nitride semiconductor light-emittingdevice can be provided.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a preferred exemplarynitride semiconductor laser device representing a nitride semiconductorlight-emitting device of the present invention.

FIG. 2 is a schematic side view of the nitride semiconductor laserdevice shown in FIG. 1, in a direction of length of a cavity.

FIG. 3 is a schematic view of a configuration of an exemplary ECRsputtering film deposition apparatus.

FIG. 4 shows results of analysis by using AES, in a direction ofthickness, of a composition of aluminum oxynitride separately fabricatedunder the conditions the same as those for a coating film in anembodiment of the present invention.

FIG. 5 shows results of theoretical calculation of reflectance spectrumat a light-emitting facet of the cavity of the nitride semiconductorlaser device in the embodiment of the present invention.

FIG. 6 shows results of actual measurement of reflectance spectrum atthe light-emitting facet of the cavity of the nitride semiconductorlaser device in the embodiment of the present invention.

FIG. 7 shows results of examination of the COD level after aging, of thenitride semiconductor laser device in the embodiment of the presentinvention.

FIG. 8 shows results of examination of dependency on the COD level, ofoxygen content in the coating film of the nitride semiconductor laserdevice in the embodiment of the present invention.

FIGS. 9A and 9B show results of theoretical calculation of reflectancespectrum at a light-emitting facet of a cavity of another exemplarynitride semiconductor laser device of the present invention

FIG. 10 shows results of examination of the COD level after aging, of anitride semiconductor laser device according to a comparative example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described hereinafter. Inthe drawings of the present invention, it is noted that the samereference characters represent the same or corresponding elements.

FIG. 1 is a schematic cross-sectional view of a preferred exemplarynitride semiconductor laser device representing a nitride semiconductorlight-emitting device of the present invention. Here, a nitridesemiconductor laser device 100 is structured such that, throughepitaxial growth, an n-type buffer layer 102 composed of n-type GaNhaving a thickness of 0.2 μm, an n-type clad layer 103 composed ofn-type Al_(0.06)Ga_(0.94)N having a thickness of 2.3 μm, an n-type guidelayer 104 composed of n-type GaN having a thickness of 0.02 μm, amultiple quantum well active layer 105 constituted of a multiple quantumwell layer composed of InGaN having a thickness of 4 nm and GaN having athickness of 8 nm and a protection layer composed of GaN having athickness of 70 nm, a p-type current blocking layer 106 composed ofp-type Al_(0.3)Ga_(0.7)N having a thickness of 20 nm, a p-type cladlayer 107 composed of p-type Al_(0.05)Ga_(0.95)N having a thickness of0.5 μm, and a p-type contact layer 108 composed of p-type GaN having athickness of 0.1 μm are successively stacked on a semiconductorsubstrate 101 composed of n-type GaN.

It should be noted that each layer has a composition ratio adjusted asappropriate and thus irrelevant to the essence of the present invention.In addition, a wavelength of a laser beam lased from the nitridesemiconductor laser device of the present embodiment can be adjusted asappropriate, for example, in a range from at least 370 nm to at most 470nm, depending on the composition ratio of multiple quantum well activelayer 105. In the present embodiment, adjustment is made such that thelaser beam at a wavelength of 405 nm is lased.

Nitride semiconductor laser device 100 is formed such that astripe-shaped ridged stripe portion 111 extends in a direction of lengthof the cavity, by partially removing p-type clad layer 107 and p-typecontact layer 108. Here, ridged stripe portion 111 has a stripe width,for example, in a range from approximately 1.2 μm to 2.4 μm, typicallyapproximately 1.5 μm. It is noted that the stripe width of ridged stripeportion 111 of nitride semiconductor laser device 100 is not limited assuch. The stripe width may be set, for example, in a range fromapproximately 2 μm to 100 μm, so that nitride semiconductor laser device100 is applicable also as a broad area type nitride semiconductor laserdevice used for illumination purposes.

Moreover, a p electrode 110 formed as a stack of a Pd layer, an Molayer, and an Au layer is provided on the surface of p-type contactlayer 108, and an insulating film 109 formed as a stack of an SiO₂ filmand a TiO₂ film is provided under p electrode 110, except for whereridged stripe portion 111 is formed. Further, an n electrode 112 formedas a stack of an Hf film and an Al film is formed on the surface ofsemiconductor substrate 101 opposite to where the above-described layersare stacked.

FIG. 2 is a schematic side view of nitride semiconductor laser device100 shown in FIG. 1, in a direction of length of the cavity. Here, acoating film 114 formed of an aluminum oxynitride film having athickness of 6 nm is formed on a light-emitting facet of cavity 113 ofnitride semiconductor laser device 100, and an aluminum oxide film 115having a thickness of 117 nm is formed on coating film 114. In addition,a silicon oxide film 122 having a thickness of 71 nm is formed onaluminum oxide film 115, and an aluminum oxide film 116 having athickness of 60 nm is formed on silicon oxide film 122. Here, in thepresent embodiment, a reflectance control film 121 is formed of aluminumoxide film 115, silicon oxide film 122, and aluminum oxide film 116.Here, coating film 114 has an index of refraction of 2.1 with respect tolight of a wavelength of 400 nm, and aluminum oxide film 115 has anindex of refraction of 1.68 with respect to light of a wavelength of 400nm. In addition, silicon oxide film 122 has an index of refraction of1.43 with respect to light of a wavelength of 400 nm, and aluminum oxidefilm 116 has an index of refraction of 1.68 with respect to light of awavelength of 400 nm. Accordingly, the reflectance at light-emittingfacet of cavity 113 with respect to the laser beam of a wavelength of405 nm lased from nitride semiconductor laser device 100 can becontrolled to approximately 30%.

Meanwhile, on a light-reflecting facet of cavity 117 of nitridesemiconductor laser device 100, an aluminum oxynitride film 118 having athickness of 6 nm, an aluminum oxide film 119 having a thickness of 117nm, and a high-reflection film 120 that is formed by stacking four pairsof a silicon oxide film having a thickness of 71 nm and a titanium oxidefilm having a thickness of 46 nm (starting from the silicon oxide film)and thereafter stacking a silicon oxide film having a thickness of 142nm on an outermost surface are successively formed. Here, aluminumoxynitride film 118 has an index of refraction of 2.1 with respect tolight of a wavelength of 400 nm, and aluminum oxide film 119 has anindex of refraction of 1.68 with respect to light of a wavelength of 400nm. Moreover, the silicon oxide film constituting high-reflection film120 has an index of refraction of 1.43 with respect to light of awavelength of 400 nm, and the titanium oxide film constitutinghigh-reflection film 120 has an index of refraction of 2.4 with respectto light of a wavelength of 400 nm. Accordingly, the reflectance atlight-reflecting facet of cavity 117 with respect to the laser beam of awavelength of 405 nm lased from nitride semiconductor laser device 100can be controlled to approximately 95%.

Alternatively, by forming a plurality of films different in indices ofrefraction other than the films structured as described above onlight-reflecting facet of cavity 117 of nitride semiconductor laserdevice 100, the reflectance of approximately 95% can be achieved. Forexample, an aluminum oxynitride film having a thickness of 6 nm and analuminum oxide film having a thickness of 117 nm are successively formedon light-reflecting facet of cavity 117 of nitride semiconductor laserdevice 100, and thereafter a stack formed by stacking 6 pairs of asilicon oxide film having a thickness of 71 nm and a tantalum oxide filmhaving a thickness of 51 nm (starting from the silicon oxide film) isformed and an aluminum oxide film having a thickness of 120 nm is formedon an outermost surface, thus forming a multi-layer film. Here, thetantalum oxide film has an index of refraction of 2.0 with respect tolight of a wavelength of 400 nm.

Alternatively, an aluminum oxynitride film having a thickness of 6 nmand an aluminum oxide film having a thickness of 117 nm are successivelyformed on light-reflecting facet of cavity 117 of nitride semiconductorlaser device 100, and thereafter a stack formed by stacking 7 pairs of asilicon nitride film having a thickness of 48 nm and a silicon oxidefilm having a thickness of 71 nm (starting from the silicon nitridefilm) is formed and a silicon oxide film having a thickness of 142 nm isformed on an outermost surface, thus forming a multi-layer film. Here,the silicon nitride film has an index of refraction of 2.1 with respectto light of a wavelength of 400 nm.

Coating film 114, reflectance control film 121, aluminum oxynitride film118, aluminum oxide film 119, and high-reflection film 120 are formed onfacet of cavity 113 and facet of cavity 117 of each sample, the samplebeing fabricated by successively stacking aforementioned nitridesemiconductor layers such as a buffer layer on the semiconductorsubstrate described above, forming the ridged stripe portion, andthereafter cleaving a wafer where the insulating film, the p electrodeand the n electrode are formed, to thereby expose cleavage planes, i.e.,facet of cavity 113 and facet of cavity 117.

Prior to forming coating film 114 and reflectance control film 121described above, facet of cavity 113 is preferably cleaned by heating toa temperature, for example, of at least 100° C. in a film depositionapparatus so as to remove an oxide film, an impurity and the likeadhered to facet of cavity 113, however, in the present invention, it isnot essential. Alternatively, facet of cavity 113 may be cleaned byirradiating facet of cavity 113, for example, with argon or nitrogenplasma, however, in the present invention, it is not essential.Alternatively, plasma irradiation while heating facet of cavity 113 maybe adopted. In plasma irradiation described above, for example, nitrogenplasma irradiation may follow argon plasma irradiation, or vice versa.Other than argon and nitrogen, for example, a rare gas such as helium,neon, xenon, or krypton may be used. Forming of coating film 114 andreflectance control film 121 to be formed on facet of cavity 113 ispreferably carried out at a heated temperature, for example, in a rangefrom at least 100° C. to at most 500° C., however, in the presentinvention, coating film 114 and reflectance control film 121 may beformed without heating.

Coating film 114 and reflectance control film 121 described above may beformed, for example, with ECR (Electron Cyclotron Resonance) sputteringwhich will be described below, however, they may be formed with othervarious sputtering methods or CVD (Chemical Vapor Deposition) or EB(Electron Beam) vapor deposition.

FIG. 3 is a schematic view of a configuration of an exemplary ECRsputtering film deposition apparatus. Here, the ECR sputtering filmdeposition apparatus includes a film deposition chamber 200, a magneticcoil 203, and a microwave introduction window 202. In film depositionchamber 200, a gas inlet port 201 and a gas exhaust port 209 areprovided, and an Al target 204 connected to an RF power supply 208 and aheater 205 are provided. In addition, in film deposition chamber 200, asample carrier 207 is provided and a sample 206 is placed on samplecarrier 207. Magnetic coil 203 is provided in order to produce magneticfield necessary for generating plasma, and RF power supply 208 is usedfor sputtering Al target 204. In addition, microwaves 210 are introducedinto film deposition chamber 200 through microwave introduction window202.

Gaseous nitrogen is introduced into film deposition chamber 200 throughgas inlet port 201 at a flow rate of 5.5 sccm, and gaseous oxygen isintroduced at a flow rate of 1.0 sccm. In addition, in order toefficiently generate plasma so as to increase a film deposition speed,gaseous argon is introduced at a flow rate of 20.0 sccm. It is notedthat the oxygen content in coating film 114 can be varied by varying aratio between the gaseous nitrogen and the gaseous oxygen in growthchamber 200. Moreover, in order to sputter Al target 204, RF power of500 W is applied to Al target 204 and microwave power of 500 W necessaryfor generating plasma is applied, whereby coating film 114 composed ofaluminum oxynitride having an index of refraction of 2.1 with respect tolight of a wavelength of 400 nm can be formed at the film depositionrate of 1.7 angstrom/second.

It is noted that contents of aluminum, nitrogen and oxygen (atomic %)forming coating film 114 can be measured, for example, with AES (AugerElectron Spectroscopy). Alternatively, content of oxygen composingcoating film 114 can be measured also with TEM-EDX (TransmissionElectron Microscopy-Energy Dispersive X-ray Spectroscopy).

FIG. 4 shows results of analysis by using AES, in a direction ofthickness, of a composition of aluminum oxynitride separately fabricatedunder the same conditions and with the same method as described above.The contents of aluminum, oxygen and nitrogen, respectively, wereobtained as based on an AES signal in intensity, with the sensitivity ofa peak of each element considered. Herein, aluminum, oxide and nitrogentogether assume 100 atomic % and an element other than aluminum, oxygenand nitrogen, contained in a small amount, such as argon, is excludedtherefrom.

As shown in FIG. 4, it can be seen that the content of aluminumcomposing aluminum oxynitride is 34.8 atomic %, the content of oxygen is3.8 atomic %, and the content of nitrogen is 61.4 atomic %, with asubstantially uniform composition in the direction of thickness. Itshould be noted that, although not shown in FIG. 4, a negligible amountof argon was detected.

Thereafter, aluminum oxide film 115 is formed on coating film 114 withECR sputtering. Here, aluminum oxide film 115 is fabricated, forexample, as follows. Initially, in the ECR sputtering film depositionapparatus shown in FIG. 3, after coating film 114 is formed, the gaseousoxygen is introduced into film deposition chamber 200 through gas inletport 201 at a flow rate of 6.5 sccm. In addition, in order toefficiently generate plasma so as to increase a film deposition speed,the gaseous argon is introduced at a flow rate of 40 sccm. Then, inorder to sputter Al target 204, RF power of 500 W is applied to Altarget 204 and microwave power of 500 W necessary for generating plasmais applied, whereby aluminum oxide film 115 having an index ofrefraction of 1.68 with respect to light of a wavelength of 400 nm isformed at the film deposition rate of 20 nm/second.

In succession, silicon oxide film 122 is formed on aluminum oxide film115 using ECR sputtering. Here, silicon oxide film 122 is fabricated,for example, as follows. Initially, in the ECR sputtering filmdeposition apparatus shown in FIG. 3, Al target 204 is replaced with anSi target. After aluminum oxide film 115 is formed, the gaseous oxygenis introduced into film deposition chamber 200 through gas inlet port201 at a flow rate of 7.5 sccm. In addition, in order to efficientlygenerate plasma so as to increase a film deposition speed, the gaseousargon is introduced at a flow rate of 20 sccm. Then, in order to sputterthe Si target, RF power of 500 W is applied to the Si target andmicrowave power of 500 W necessary for generating plasma is applied,whereby silicon oxide film 122 having an index of refraction of 1.43with respect to light of a wavelength of 400 nm is formed at the filmdeposition rate of 20 nm/second.

Thereafter, aluminum oxide film 116 is formed on silicon oxide film 122using ECR sputtering. Here, aluminum oxide film 116 is fabricated, forexample, as follows. Initially, in the ECR sputtering film depositionapparatus shown in FIG. 3, the Si target used for forming silicon oxidefilm 122 is replaced with the Al target. Then, the gaseous oxygen isintroduced into film deposition chamber 200 through gas inlet port 201at a flow rate of 6.5 sccm. In addition, in order to efficientlygenerate plasma so as to increase a film deposition speed, the gaseousargon is introduced at a flow rate of 40 sccm. Then, in order to sputterthe Al target, RF power of 500 W is applied to the Al target andmicrowave power of 500 W necessary for generating plasma is applied,whereby aluminum oxide film 116 having an index of refraction of 1.68with respect to light of a wavelength of 400 nm is formed at the filmdeposition rate of 20 nm/second. Thus, reflectance control film 121constituted of aluminum oxide film 115, silicon oxide film 122, andaluminum oxide film 116 is formed on coating film 114.

Aluminum oxynitride film 118, aluminum oxide film 119, andhigh-reflection film 120 on light-reflecting facet of cavity 117 canalso be formed with ECR sputtering, as in the case of coating film 114and the like. Here, before forming these films, preferably, cleaningthrough heating and/or cleaning with plasma irradiation is alsoperformed. It is noted here that deterioration of the light-emittingportion gives rise to a problem on the light-emitting side where opticaldensity is great, whereas deterioration does not cause a problem on thelight-reflection side in many cases because optical density is smalleron the light-reflection side than on the light-emitting side. Therefore,in the present invention, it is not necessary to provide a film such asan aluminum oxynitride film on light-reflecting facet of cavity 117. Inaddition, in the present embodiment, aluminum oxynitride film 118 havinga thickness of 6 nm is formed on light-reflecting facet of cavity 117,however, aluminum oxynitride film 118 may have a greater thickness, forexample, of 50 nm.

After the films described above are formed on light-emitting facet ofcavity 113 and light-reflecting facet of cavity 117, heat treatment maybe performed. Thus, removal of moisture contained in the films orimprovement in film quality through heat treatment can be expected.

As described above, coating film 114, aluminum oxide film 115, siliconoxide film 122, and aluminum oxide film 116 are successively formed onlight-emitting facet of cavity 113 of the sample, and aluminumoxynitride film 118, aluminum oxide film 119, and high-reflection film120 are successively formed on light-reflecting facet of cavity 117.Thereafter, the sample is divided into chips, to thereby obtain nitridesemiconductor laser devices 100 shown in FIG. 1.

FIG. 5 shows results of theoretical calculation of reflectance spectrumat light-emitting facet of cavity 113 of nitride semiconductor laserdevice 100 structured as described above. It can be seen from FIG. 5that high reflectance of approximately 30% with respect to light of awavelength of 405 nm can be obtained at light-emitting facet of cavity113 of nitride semiconductor laser device 100.

FIG. 6 shows results of actual measurement of reflectance spectrum atlight-emitting facet of cavity 113 of nitride semiconductor laser device100 structured as described above. It can be seen from FIG. 6 that highreflectance of approximately 30% with respect to light of a wavelengthof 405 nm can be obtained at light-emitting facet of cavity 113 ofnitride semiconductor laser device 100, which is substantially the sameas the theoretical calculation result shown in FIG. 5.

The theoretical calculation result of reflectance spectrum shown in FIG.5 was obtained by theoretical calculation based on measurement of athickness and an index of refraction with respect to light of awavelength of 400 nm n, of each layer forming nitride semiconductorlaser device 100. Here, the thickness and the index of refraction withrespect to light of a wavelength of 400 nm of each layer constitutingnitride semiconductor laser device 100 were found using ellipsometry. Inaddition, the actual reflectance spectrum shown in FIG. 6 was foundbased on spectroscopy of white light and measurement of reflectance withrespect to light of each wavelength.

The COD level after aging (80° C., CW drive, optical output of 40 mW,300 hours) of nitride semiconductor laser device 100 described above wasexamined, and the results are as shown in FIG. 7. As shown in FIG. 7, itwas found that the COD level after aging of nitride semiconductor laserdevice 100 was very high around 350 to 400 mW.

Alternatively, a nitride semiconductor laser device according to acomparative example, having a structure the same as nitridesemiconductor laser device 100 except that reflectance control film 121as above was directly formed on light-emitting facet of cavity 113without coating film 114, was fabricated. Then, the COD level afteraging (80° C., CW drive, optical output of 40 mW, 300 hours) of thenitride semiconductor laser device according to the comparative examplewas examined. The results are as shown in FIG. 10. As shown in FIG. 10,it was found that the COD level after aging of the nitride semiconductorlaser device according to the comparative example was approximately 200to 250 mW, which is significantly lower than that of nitridesemiconductor laser device 100 described above.

The reason why the COD level after aging of nitride semiconductor laserdevice 100 was thus higher than that of the nitride semiconductor laserdevice according to the comparative example may be because the number ofnonradiative centers at an interface between light-emitting facet ofcavity 113 and coating film 114 decreased as a result of formation ofcoating film 114 on light-emitting facet of cavity 113 and/or becauseclose contact between light-emitting facet of cavity 113 and coatingfilm 114 was attained.

Thereafter, dependency on the COD level of the oxygen content in coatingfilm 114 of nitride semiconductor laser device 100 was examined. Theresults are as shown in FIG. 8. Here, the oxygen content in coating film114 was varied from O atomic % to 50 atomic %, and the COD level ofnitride semiconductor laser device 100 after aging for 300 hours (300hours, 80° C., optical output of 100 mW, CW drive) was measured. Here,when the oxygen content in coating film 114 is varied, the content ofaluminum (atomic %) in coating film 114 hardly varies and the content ofnitrogen (atomic %) decreases in correspondence with increase in thecontent of oxygen (atomic %), because both of oxygen and nitrogen canbasically bond to aluminum.

As shown in FIG. 8, it can be seen that, when the oxygen content incoating film 114 is in a range from at least 0 atomic % to at most 35atomic %, in particular when the oxygen content in coating film 114 isin a range from at least 2 atomic % to at most 30 atomic %, the CODlevel tends to be very high at 300 mW or greater. Therefore, the oxygencontent in coating film 114 formed on light-emitting facet of cavity 113is preferably in a range from at least 0 atomic % to at most 35 atomic %and more preferably in a range from at least 2 atomic % to at most 30atomic %, in which case the COD level after aging tends to improve.Naturally, when the oxygen content in coating film 114 is set to 0atomic %, coating film 114 is formed of an aluminum nitride film, andwhen the oxygen content is greater than 0 atomic %, coating film 114 isformed of an aluminum oxynitride film.

As shown in FIG. 8, the reason why the COD level can be high when theoxygen content in coating film 114 formed on light-emitting facet ofcavity 113 is in a range from at least 0 atomic % to at most 35 atomic %may be because close contact between facet of cavity 113 formed of anitride semiconductor and coating film 114 is improved and generation ofnonradiative recombination level due to oxidation of facet of cavity 113does not affect the COD level.

When the oxygen content is set to 0 atomic %, the COD level is slightlylower. This may be because aluminum nitride composing coating film 114has large internal stress and contact between facet of cavity 113 andcoating film 114 becomes weaker. The present inventors, however, havefound that the COD level improves when silicon nitride is contained incoating film 114 composed of aluminum nitride. This may be becausesilicon nitride mitigates the internal stress of aluminum nitride.

In addition, if the oxygen content in coating film 114 is greater than35 atomic %, it is considered that a part of facet of cavity 113 formedof a nitride semiconductor is oxidized by oxygen contained in coatingfilm 114 and such oxidation results in nonradiative recombination level,which has led to lower COD level.

FIG. 9A shows results of theoretical calculation of reflectance spectrumat light-emitting facet of cavity 113 of another exemplary nitridesemiconductor laser device, that is structured similarly to nitridesemiconductor laser device 100 described above except that coating film114 formed of an aluminum nitride film having a thickness of 24 nm, asilicon oxide film having a thickness of 64 nm, an aluminum nitride filmhaving a thickness of 24 nm, and an aluminum oxide film having athickness of 24 nm are successively formed on light-emitting facet ofcavity 113. Here, the aluminum nitride film has the index of refractionof 2.1 with respect to light of a wavelength of 400 nm, the siliconoxide film has the index of refraction of 1.43 with respect to light ofa wavelength of 400 nm, and the aluminum oxide film has the index ofrefraction of 1.68 with respect to light of a wavelength of 400 nm.

FIG. 9B shows results of theoretical calculation of reflectance spectrumat light-emitting facet of cavity 113 of another exemplary nitridesemiconductor laser device, that is structured similarly to nitridesemiconductor laser device 100 described above except that coating film114 formed of an aluminum nitride film having a thickness of 3 nm, analuminum oxide film having a thickness of 117 nm, a silicon oxide filmhaving a thickness of 71 nm, an aluminum oxide film having a thicknessof 60 nm, a silicon oxide film having a thickness of 71 nm, and analuminum oxide film having a thickness of 60 nm are successively formedon light-emitting facet of cavity 113. Here, the aluminum nitride filmhas the index of refraction of 2.1 with respect to light of a wavelengthof 400 nm, the aluminum oxide film has the index of refraction of 1.68with respect to light of a wavelength of 400 nm, and the silicon oxidefilm has the index of refraction of 1.43 with respect to light of awavelength of 400 nm.

As can clearly be seen from comparison of FIGS. 5, 9A and 9B, thereflectance can be controlled by varying film structure onlight-emitting facet of cavity 113.

It is noted that aluminum oxynitride discussed in the present inventionmay take any form in the present invention; aluminum oxide may be mixedin AlN, crystals of aluminum oxynitride may be present in AlN, oraluminum oxide and aluminum oxynitride may be present in AlN.

In the embodiment above, an example where the oxygen content in thecoating film composed of aluminum oxynitride is substantially uniform inthe direction of thickness has been described, however, a coating filmhaving a multi-layer structure with the oxygen content gradually variedor different in the direction of thickness may be formed.

Meanwhile, in the embodiment above, preferably, coating film 114 has athickness of at least 1 nm. If coating film 114 has a thickness lessthan 1 nm, it becomes difficult to control the thickness of coating film114, and coating film 114 may not be formed on light-emitting facet ofcavity 113. On the other hand, even when the thickness of coating film114 is too large, it is assumed that the effect of the present inventionis not impaired, although internal stress of coating film 114 may giverise to a problem. From the point of view of improvement incontrollability of the thickness of coating film 114 and controllabilityof the reflectance at light-emitting facet of cavity 113, coating film114 preferably has a thickness in a range from at least 3 nm to at most50 nm.

The COD level of nitride semiconductor laser device 100 described aboveis significantly affected by coating film 114 on light-emitting facet ofcavity 113, but not much affected by reflectance control film 121 oncoating film 114. Therefore, in the present invention, reflectancecontrol film 121 can be designed relatively freely, taking intoconsideration only the reflectance at light-emitting facet of cavity113, and hence the degree of freedom in design remarkably improves.

In addition, in the embodiment above, if coating film 114 is formed ofan aluminum oxynitride film, coating film 114 may also be formed, forexample, with reactive sputtering, by providing a target composed ofaluminum oxide in the film deposition chamber and introducing solelygaseous nitrogen into the film deposition chamber. If such a targetcomposed of aluminum oxide is employed, the aluminum oxynitride film canbe formed without intentionally introducing gaseous oxygen into the filmdeposition chamber.

In addition, in the embodiment above, in forming coating film 114 formedof an aluminum oxynitride film, as aluminum is highly prone tooxidation, control and reproduction of a composition of oxynitride lowin oxygen content tends to be difficult when gaseous oxygen isintroduced in the film deposition chamber. Here, however, by usingaluminum oxide less oxidized and represented in a compositional formulaAl_(x)O_(y) (0<x<1, 0<y<0.6, x+y=1) as a target and by introducingsolely gaseous nitrogen but not gaseous oxygen into the film depositionchamber, the aluminum oxynitride film low in oxygen content canrelatively easily be formed. Moreover, a similar effect is obtained alsowhen a target composed of aluminum oxynitride low in oxygen content isemployed instead of the aforementioned target composed of aluminum oxideless oxidized and represented in a compositional formula Al_(x)O_(y)(0<x<1, 0<y<0.6, x+y=1).

In addition, the oxygen content in the aluminum oxynitride film can bevaried also by varying film deposition conditions such as a degree ofvacuum and/or a film deposition temperature in the film depositionchamber, whereby the composition of the aluminum oxynitride film can bevaried. It is noted that a smaller degree of vacuum in the filmdeposition chamber leads to a result that an oxide is more readily takeninto the aluminum oxynitride film, while a higher film depositiontemperature leads to a result that an oxide is less likely to be takeninto the aluminum oxynitride film.

If film is deposited with sputtering using a target composed of Al (Altarget) with the introduction of gaseous argon and gaseous nitrogen intothe film deposition chamber after an inner wall of the film depositionchamber is oxidized or aluminum oxide is formed on the inner wall of thefilm deposition chamber, the inner wall of the film deposition chamberhas oxygen departed because of plasma, and therefore, coating film 114formed of the aluminum oxynitride film can be formed.

In the present invention, for example, a nitride semiconductor mainlycomposed of (at least 50 mass % of the total) AlInGaN (a compound of atleast one group III element selected from the group of aluminum, indiumand gallium and nitrogen representing group V elements) may be employedas the nitride semiconductor.

In the present invention, reflectance control film 121 is notparticularly limited provided that it is formed of an oxide. Amongothers, however, a stack of an aluminum oxide film and a silicon oxidefilm is preferably used as reflectance control film 121. If reflectancecontrol film 121 is formed of the stack of the aluminum oxide film andthe silicon oxide film, fluctuation in the reflectance at light-emittingfacet of cavity 113 with respect to fluctuation in the thicknesses ofrespective films constituting reflectance control film 121 is small, andtherefore, the reflectance can be reproduced with excellentcontrollability. In the present invention, it is noted that the stack ofthe aluminum oxide film and the silicon oxide film constitutingreflectance control film 121 may be formed in such a manner that atleast one aluminum oxide film and at least one silicon oxide film arealternately stacked.

In addition, in the present invention, the reflectance at light-emittingfacet of cavity 113 with respect to laser beams (laser beam of awavelength, for example, in a range from at least 370 nm to at most 470nm) lased from nitride semiconductor laser device 100 is preferably atleast 18%, more preferably at least 30%, and further preferably at least40%. When the reflectance at light-emitting facet of cavity 113 is 18%or greater, generally, optical density at facet of cavity 113 isincreased and it is less likely that high COD level is obtained. In thepresent invention, however, as the coating film formed of the aluminumoxynitride film or the aluminum nitride film is formed on facet ofcavity 113, it is likely that high COD level is obtained. On the otherhand, when the reflectance at light-emitting facet of cavity 113 is 30%or greater, in particular 40% or greater, fluctuation in the reflectancewith respect to thickness of each film constituting reflectance controlfilm 121 can be made smaller by forming reflectance control film 121with the stack of the aluminum oxide film and the silicon oxide film.Thus, it is likely that yield is improved.

The present invention is suitably used, for example, for a nitridesemiconductor light-emitting device such as a nitride semiconductorlaser device lasing at a wavelength in ultraviolet to green range, anitride semiconductor laser device of a broad area type having a stripeof several tens μm in width and used for high-output applications, anitride semiconductor light-emitting diode device lasing at a wavelengthin ultraviolet to red range, or the like.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1.-9. (canceled)
 10. A nitride semiconductor light-emitting devicecomprising a coating film formed on a facet of a nitride semiconductor,wherein said coating film is formed of an aluminum oxynitride film or analuminum nitride film, and oxygen content in said coating film varies inthe direction of thickness of said coating film, and said oxygen contentin said coating film is in a range from at least 0 atomic % at most 35atomic %.
 11. The nitride semiconductor light-emitting device of claim10, wherein a reflectance control film formed of an oxide is formed onsaid coating film.
 12. A nitride semiconductor light-emitting deviceaccording to claim 10, wherein the thickness of said coating film is noless than 1 nm and no more than 50 nm.